Task specific effects of fatigue on lower limb muscle synergies during single and double leg drop jumps in female athletes.

BACKGROUND

Drop jump (DJ) tasks are widely used to assess lower-limb neuromuscular function and injury risk. Fatigue is a key factor elevating injury risk, yet its effects on neuromuscular control during single-leg drop jumps (SLDJ) and double-leg drop jumps (DLDJ), and whether these effects differ by task type, remain poorly understood.

METHODS

Fifteen female athletes performed SLDJ and DLDJ before and after a standardized fatigue protocol. Surface electromyography signals from nine lower-limb muscles were collected. Muscle synergies were extracted via non-negative matrix factorization, and synergy similarity was assessed using scalar product and Pearson correlation coefficients. Linear mixed-effects models examined differences in muscle contributions and temporal activation features.

RESULTS

Three muscle synergy modules were consistently identified across both tasks and fatigue conditions, with high inter-module similarity (scalar product and Pearson r > 0.80). Synergy structure remained stable regardless of task or fatigue, while task type and fatigue selectively modulated specific muscle contributions. Notably, vastus lateralis contribution showed opposing fatigue-related trends between tasks, and lateral gastrocnemius contribution decreased significantly after fatigue in SLDJ only.

CONCLUSIONS

The central nervous system maintains a stable modular control strategy across DJ tasks and fatigue conditions. Adaptations to fatigue manifest primarily through task-specific modulation of intra-module muscle weights rather than restructuring of synergy organization. SLDJ demonstrated greater neuromuscular sensitivity to fatigue than DLDJ, indicating that single-leg landing tasks may be more susceptible to fatigue-induced alterations in neuromuscular control. These findings inform neuromuscular screening and targeted training strategies for female athletes.